1. Field of the Invention
The present invention relates to cementing subterranean zones penetrated by well bores with cement compositions having enhanced compressive strengths.
2. Description of the Prior Art
Subterranean zones penetrated by well bores are commonly sealed by hydraulic cement compositions. For example, hydraulic cement compositions are used in primary cementing operations whereby strings of pipe such as casings and liners are cemented in well bores. In performing primary cementing, a hydraulic cement composition is pumped into the annular space between the walls of a well bore and the exterior surfaces of a pipe string disposed therein. The cement composition is permitted to set in the annular space thereby forming an annular sheath of hardened substantially impermeable cement therein which supports and positions the pipe string in the well bore and seals the exterior surfaces of the pipe string to the walls of the well bore. Hydraulic cement compositions are also utilized in a variety of cementing operations such as sealing highly permeable zones or fractures in subterranean zones, plugging cracks or holes in pipe strings and the like.
In all of the various cementing operations in subterranean zones which utilize hydraulic cement compositions, the cement compositions must have sufficient compressive strengths to resist cracking or shattering as a result of pipe movements, impacts and/or shocks subsequently generated by drilling and other well operations. The cement sheath in the annulus between a pipe string and the walls of a well bore often fails by cracking or shattering and the seal between the pipe string and well bore is lost.
Light weight cement compositions are utilized in subterranean zones which are unconsolidated or otherwise subject to fracturing at relatively low hydrostatic pressures. Light weight foamed cement compositions are also utilized in wells to prevent excessive hydrostatic pressure from being exerted on subterranean zones. In addition, a foamed cement composition contains compressed gas which improves the ability of the composition to maintain pressure and prevent the flow of formation fluids into and through the cement composition during its transition time, i.e., the time during which the cement composition changes from a true fluid to a hard set mass. Foamed cement slurries are also advantageous because they have low fluid loss properties.
While the heretofore utilized cement compositions, light weight cement compositions and light weight foamed cement compositions have been utilized successfully heretofore, failures often occur due to the cement compositions not having high enough compressive strengths at the high temperature and pressure conditions of the subterranean zones being cemented. Thus, there are continuing needs for improved subterranean zone normal weight cement compositions, light weight cement compositions and foamed cement compositions which have enhanced compressive strengths.